Planet Earth

According to the CSET test guide, there will be a total of 50 multiple choice questions and three constructed response questions for CSET 122.

a. Diagram the major divisions of the geologic time scale as a basis for understanding changes in the Earth's processes

Precambrian- fist 4 billion year of Earth, 88% of Earths' history. This era is divided into the Achaean eon (ancient age) and Proterozoic eon (early life). Earth's first crust was probably basalt, hot turbulent mantle, probably recycled most of this material back into the mantle, perhaps over and over again. Formation of the continental crust, some type of plate-like motion, hot spot volcanism (shield volcanism and oceanic plateaus). Large continental masses was accomplished through the collision and accretion of various types of terrains. Within the deepest regions of these collision zones, partial melting and the thickened crust generated silica-rich magmas that ascended and intruded the rocks above. Results were large crustal provinces that accredit with others to form large crustal blocks called cratons. The assembly of large craton involved several mountain building episodes such as when Indian subcontinent collided with Asia. About 3 million years ago, the craton became large and thick to resist direct reincorporation in to the mantle. By the end of the Precambrian, about 85% of the modern continental crust had formed. 3-2.5 million years ago accretion of numerous island arcs and other crustal fragments generated several large crustal provinces, which North America contains some of. 1.1 billion years ago a super landmass, Rodinia, formed. Between 800-600 million years ago, it split apart. By the end of the Precambrian, many had resembled to produce Gondwana (north America, North Europe, and Sibera wasn't part of it). Life first evolved (within the ocean) around vents-prokaryotes were the only living things on Earth.

Proterozoic Glaciation

During the Cryogenia and Edicarian Period of the Neoproterozoic Era, the world saw at least two episodes of global glaciation. Most of the land mass was situated at the equator. Since the polar regions receive less solar radiation (and no land mass to absorb the UV radiation) then these regions began to cool significantly. The little outgassing warming effects of the greenhouse gases were not enough to counter the cooling of the polar regions. A runaway freezing quickly and repeatedly enveloped the planet in ice, reaching all the way to the equator (which has never happened again). This event is known as the Snowball Earth hypothesis. Evidence for the repeated global freezing:

1) Variation of the carbon-13: carbon-12 in the life activities, so limestone formed during this time was heavily enriched in carbon-13. So, a finding of high levels of carbon-12 in sediment has been interpreted to mean that the deep freeze conditions had killed off most or nearly all of the marine photosynthetic life forms in the water and incorporate their remains in the sediment.

2) Another proof of the Snowball Earth are the BIF that were able to form during this time as a consequence of an oxygen-depleted planet. Oxygen was depleted as a result of nearly all of the photosynthesizing life forms being wiped out.

3) Carbonic rocks that capped the glacial sequences. Carbonic rocks normally form in warm water. Carbon dioxide rapidly accumulated in the atmosphere. Eventually, enough warming in the tropics took place that caused the sea ice to melt. And because sea water has a lower albedo, then more sun's radiation was absorbed, which led to even more warming at the equator. Rain washed carbon dioxide from the atmosphere onto the silicate rocks of the continental crust (which acted as a weak solution of carbonic acid) and freed the silicate rocks of calcium, magnesium, and other ions. These ions washed into the ocean and recombined to form layers of carbonate rocks, which deposited over glacial till. As the carbonate rocks continued to buildup, it began to deplete carbon dioxide from the atmosphere. So, as a result, the Earth cooled and froze over again. This cycle of carbon dioxide increasing-warming-rain-carbonate buildup-depleting of carbon dioxide-refreeze went on until the continents near the equator moved to higher latitudes. Because of this, the prerequisite for the operation of a Snowball Earth was eliminated.

As the glaciers receded and an abundant of carbon dioxide, there was an explosion in the evolution of diverse and complex multicellular animals that took place.

Proterozoic Life Forms

During the Archean Eon, life was dominated by prokaryotes. The first direct evidence of eukaryotes appears in the Proterozoic Eon rocks. Simple eukaryotes may have first evolved during the Archean, but were so minor in Earth's biota. The introduction of eukaryotes opened up the world for sexual reproduction and genetic recombination. Multicellular eukaryotes first appeared in the Proterozoic Eon. At the beginning of the Proterozoic Eon, prokaryotes were the dominant life forms on Earth. Life forms found during this eon includes cyanobacteria (which were found as stromatolites or thrombolites), coated grains (ooids and oncolites). Distinguishing between prokaryotes and eukaryotes is not always easy.

Eukaryotes evolved perhaps through endosymbiosis (where one organism resides in another). Nearly all eukaryotes contain mitochondria. Mitochondria's DNA and RNA is different from the DNA and RNA in the cell in which they reside. Therefore, it is through that mitochondria was once an independent prokaryote organism that was captured by other organism cells. Because mitochondrias were resistant to the digestive process, they were eventually able to adapt to life as endosymbiosis and then eventually as a cell organelle.

Plant-like protists (earliest eukaryotes) until the Ediacaran Period of the Neoprotozoic Era, most organisms were microscopic. During the Ediacaran Period, a group of fossils were found and were between the seize of 1 cm up to 50 cm or more. These fossils are called the Ediacaran Biota. These fossils are found on all modern continents except Antarctica. These are multicellular animals (metazoans). These organisms had soft bodies, which may have been useful for mobility, but provided little protection against predators. So, during the Ediacaran Period, an organisms called the cloudinids evolved small conical skeleton that were made out of hard calcium carbonate.

Proterozoic Super continents

The beginning of this Eon marks the beginning of the platform phase of Earth's history. Cratons no longer expanded. Modifications to cratons occurred through accretion, suturing during collision, separation along rifts, and sediment deposition. The first supercontinent was Rodinia and was fully assembled in the Mesoproterozoic Era. Rodinia was made up of Laurentia, North America-Greenland craton, Australian and East Antarctic craton, Baltica craton, Siberian craton, North and South China craton, and other pieces of continental crust. Rodinia began to split 800 to 700 mya, which opened up the Pacific Ocean. Small crustal pieces sutured together in a tectonic event called the Pan-African Orogeny to form the craton of Africa. During Neoproterozoic Era, Laurentia and eastern Gondwana came together on opposite side of African craton and formed a second supercontinent called Pannotia. Pannotia separated at the end of the Neoproterozoic Era.

Proterozoic Oxygenation of atmosphere and Ocean

There was a small amount of free oxygen as a result of the breakdown of water molecules by the UV radiation. 3.5 bya, cyanobacteria began releasing oxygen into the ocean. BIF form in oxygen-depleted environment. BIFs formed until about 1.9 bya. Then, redbeds formed during a time of oxygen rich environment.

Phanerozoic Eon

Paleozoic era

Several times, shallow seas moved inland and receded, leaving sandstones. Major event was the formation of Pangaea. North America, Europe, and Siberia joined to form Laurasia. This landmass was located in the tropics where wet lands led to the formation of swamps (ultimately became the coal). By the end of the Paleozoic, Gondwana had migrated northward to collide with Lauraisa and formed the supercontinent Pangaea. Norther Europe (mainly Norway) collided with Greenland to produce the Caledonian mountains. The Cambrian period marks the beginning of the Paleozoic era (approximately 542 million years ago). This time span saw the emergence of new marine animal forms. All major invertebrates made their appearance (jellyfish, sponges, worms, mollusks, arthropods). This huge expansion in biodiversity is often referred to as Cambrian explosion. One reason for this is thought to be due to the lack of fossil record from the Precambrian era (soft bodied). In the Cambrian marks the first time organisms developed hard parts and were able to fossilize. Golden age of trilobites.

Cambrian Period:

Paleoclimate: There were was an ice age during the Late Proterozoic and Ordovician. During these two ice ages, the global temperature dropped and led to mass extinctions. During the Cambrian period, however, there was no ice formation as none of the continents were located at the poles. So, during the beginning of the Cambrian period, as the ice age was ending and the ice was retreating, sea level rose and lowland areas were flooded. Much of the world ended up being covered by epeiric seas. Marine invertebrates took advantage of these new habitat niches and radiated and flourished.

Tectonic activites: This period follows the Vendian period (during the time when the continents had been joined together as a superintendent called Rodinia). Rodinia began to break up into smaller fragments during the beginning of the Cambrian period. Continents included Gondwana (North and South China, Australia, Africa, South America, Antarctica, India, and Madagascar), Laurentia (North America and Greenland), Siberia, and Baltica (eastern Europe, Russia, and Scandinavia). The rest of Europe and Asia were in fragments along the coast of Gondwana. Laurentia was found along the equator. Baltica and Siberia were southeast of this continent.

Plant/Animal Life: Trace fossils show that animals and plants may have ventured onto land. Aniamls may have wandered onto land to perhaps lay eggs. Plants and animals may have just been washed ashore. Evidence that plants moved onto land was found at the Grand Canyon where spores of primitive land plants were found.

Oxygen first began mixing into the world's oceans in significant quantity. The oxygen-depleting bacteria were reduced and as a result allowed high levels of oxygen into the oceans. The dissolved oxygen became available to the animals and may have triggered the “Cambrian Explosion”. 90% of the organisms did not have hard parts. Thus, where hard part bearing organisms were fossilized, most of the soft-bodied organisms were filtered out of the fossil record. So, the most abundant and diverse organisms are represented by a weak fossil record. This is known as a Preservation Paradox.

Most of the major new animal groups took place during the Tommotion and Atdabanian stages of the Early Cambrian period. Many major groups of organisms appeared during this 40 million time span. Fossil records indicate that numerous organisms began to emerge and evolved resistant skeletons or coverings that were preserved as fossils. Animals that let good fossil records include trilobites, brachiopods, mollusks, hyloliths, echinoderms, and siliceous sponges. All of these could biomineralize their skeleton. Biominerlization is a process where living organisms produce minerals that harden their tissues. With an increase in marine life cam an increase in these animals seeking new ecological niches that haven't been filled yet and developing new strategies such as hunting, burrowing into sediment, and making complex burrows. Many organisms began to dig deeper into the sediment layer either to hide from predators or as a dwelling. Changes in the sediment is called the Cambrian Substrate Revolution.

Cambrian extinctions took place at least 3 times. These extinctions were followed by evolutionary recoveries.

Ordovician Period:

Sea Levels: Global sea levels rose to the highest levels recorded in history. Sea levels have been rising since the Ediacaran Period of the Proterozoic Eon. Sea levels eventually dropped before the end of the early Ordovican. Global temperatures had dropped and the ice cap in southern Gondwana was expanding. The effect of climate change on the biosphere was catastrophic and resulted in one of the most severe mass extinctions in Earth's history.

Tectonic Activities: Tectonic plate movements resulted in Laurentia moving counterclockwise across the equator and Siberia moved northward. Subduction between Laurentia, Baltica, and Gondwana resulted in the shrinking of the Iapetus Ocean. Volcanic activity along the subduction zones were the largest of the whole Phanerozoic Eon. Orogensis on Laurentia resulted in the formation of the Taconic Mountains. Closure of the Iapetus Ocean resulted in the collision of island volcanoes and other crustal pieces, including Avalonia, with Laurentia. This addition of continental margin is called the tectonostratigraphic terranes. Continental plates began moving northward. Ocean currents changed as a result. During the late Ordovician, massive glaciers formed and caused sea levels to severely drop, which caused a regression of ocean waters which drained all craton platforms. This event may have caused a mass extinction in which 60% of all marine invertebrates and 25% of all families. Ordiovician rocks have a thick line of lime and other carbonate rocks (that accumulated in shallow subtidal and intertidal environments).

Animal/Plant Life: At the end of the Cambrian Period, there was a mass extinction that was followed by a period of recovery. The Ordovician marked the appearance of abundant cephaopds- highly developed mollusks that became the first large predator. Thus, predators lifestyles drove the early diversification of animals. The evolution of efficient movement was associated with evolution of greater sensory capabilities and a more complex nervous system. Animal life that formed during this period includes: echinoderms and bryozoans. The Ordovician Period gave rise to the earliest land plants. These were tied to wet environments, reproduced by spores and had no connective tissues. They had to evolve to gravity and wind and water. They were leafless, vertical spikes.

Silurian Period:Paleoclimate: Stabilization of earth's general climate. Glacial formations melted, which resulted in a rise of sea levels.

Tectonic activities: In the beginning of the Silurian, Taconic mountain building had ceased in Laurentia and due to erosion, little of the mountain remained. Baltica collided with Laurentia. This collision is called the Caledonia orogeny. Gondwana was located in the southern polar region, surrounded by six continents. The Rodinian landmass became fragmented and began to migrate toward the equator (eventually combining again to form Laurussia and Laurasia. Orogenic events took place in eastern North America and Northwestern Europe. This resulted in the Caledonia Orogeny.

Animal/Plant Life: Glaciation at the end of the Ordovician caused many of the marine invertebrates to die out. However, a recovery came quickly and at this time, marine waters flooded the shelf areas, which opened up niches and habitats. Marine life underwent a second great ecologic revolution called the Mid-Paleozoic marine revolution. Predators and preys continued to evolve. This was a remarkable time in the evolution of fish. The first jawed fish made their appearance in this time period. The earliest jawed fish were called acanthodians and they lived in both marine and freshwater regions.

Animals and plants appeared on land during the Paleozoic Era and a complete transition to land appeared to have been successful by the end of the Silurian Period. Plants and animals had many challenges to overcome in order to adapt to life on land. However, once they were able to adapt and evolve, these organism were able to fill new niches and habitats on land. Problems that plants and animals had to overcome where: exchanges of gases, maintaining osmotic balance, maintain support of the body and dealing with gravity on land, internal temperature regulation and prevention of drying out, and protection of developing embryos.

Plants developed new features as they adapted to life on land such as: stomatas (regulated gases), roots, development of vascular tissues, formation of epicuticle layer and bark (slow internal fluids to the outside), and adopted strategies of shielding their spores or seeds until ready to be released. The first vascular land plants found so far were rhyniophytes and gave rise to other vascular plants before they became extinct in the Carboniferous Period.

Devonian Period:Paleoclimate: Toward the end of the Devonian Period, global cooling and glaciation took place. Reasons for this cooling may be due to the fact that forests were first forming on land and there was a reduction of carbon dioxide in the atmosphere. A drop in sea levels resulted and is one of the theories as to what may have caused a mass extinction, affecting most of the warm water marine animals.

Tectonic Activities: Avalonia rammed into eastern Lauentia (combining to form Euramerica) forming the Acadian Mountains called the Acadian orgogeny. When North America and Europe combined, it gave rise to the Appalachian Mountains. Euramerica and Gondwana were moving towards each other, which would eventually form Pangaea. Subduction between the Klamath Arch and western Euramerica resulted in the Antler orogeny and can the results can still be seen in the Great Basin region (which is Nevada and surrounding areas).

Animal/Plant Life: The fish continued to diversify so much and so great that this Period is called the “Age of Fishes”. Placoderms, sharks, rays, lungfishes, coelacanths, and ray-finned fishes made their appearance in this period and continued to survive to the present (except for the placoderms who survived only until the Carboniferous Period). Ammonoids appeared in this period and with their powerful jaws, they became some of the most significant marine predators.

The first efficient land plant that had roots, leaves, vascular system were the lycopoids. Vegetation consisted primarily of small plants. By the end of the Devonian, seed plants had also appeared, producing the first trees and the first forests. In the beginning, through, most of the vegetation on land began to spread. End of Devonian fossil record indicates the existence of forests with trees tens of meters tall. Plants at the end of the Devonian had leaves and roots and were taller than their predecessors. By the end of the Devonian, the first seeded plants had appeared. This rapid expansion and growth of plants has been called “Devonian Explosion”. Many changes began to take place with trees forming on land. The changes that took place were: 1) stabilization of soil by the root system, 2) increased rate of biochemical weathering on land- resulted in weathering of bedrock and formation of soil, 3) opening of new habitats for animals as they also ventured onto land. One of the greatest evolutionary success story was when insects developed wings. During Devonian, fish evolved to be fastest swimmers and possessed more acute senses and larger brains. During Devonian, fishes called lobe-finned fish began to adapt to terrestrial environment (which gave rise to the first tetrapds). They evolved into air breathing amphibians. Tetrapods (land living vertebrates) and arthropods also began moving onto land.

Carboniferous Period (Pennsylvanian and Mississippian):The name Carboniferous came from the fact that rich deposits of coal was first developed during this time period. The Carboniferous period is known for its coal swamps, which produced coal.

Paleoclimate: The Carboniferous Period is subdivided into the Pennsylvanian and Mississippian sub-periods. In the early part of the Carboniferous Period, there was a greenhouse warming period that was followed by a cooling series of rapid glacial cycles. Sea levels fluctuated rapidly, which were tied to the glacial episodes. The Mississippian Period was warm and had high sea levels which caused a flooding of the continental shelves. Then, during the mid-Carboniferous Period, the planet began to change from the greenhouse world to an icy world, which continued into the Permian Period. These changes from a warm planet to a cooler planet is known as the Milankovitch cycle. According to Milankovitch, these changes in the temperature is linked to the changes in Earth's orbital patterns in respect to the sun.http://www.emporia.edu/earthsci/student/howard2/theory.htm

Tectonic Activities: During the Carboniferous Period, Gondwana moved northward and collided with small terranes (that now make up the southern region of Europe) and Euramerica. Mountain building events that took place were the Hercynian (between Europe and northwestern Africa), Alleghanian, also called Appalachian, orogeny (Laurentia), and the Ouachita orogeny (southern region of Euramerica and Gondwana). Tectonic motion shifted present day America over the south pole, which developed a sheet of ice (known as Gondwanide glaciation). This took place during the Pennsylvanian Period.

Plant/Animal Life: Life during the Carboniferous Period was somewhat similar to that of the Devonian Period. During the Mississippian Period, encrinites were very abundant in the marine environment. On land, an extensive wetlands flourished in the tropical regions, which can be referred to as coal swamps. Reptiles and synapsids appeared in the late Carboniferous Period.

PERMIAN PERIODPaleoclimate: Sea levels rose as the buildup of glaciers began to melt. Global sea levels were high at the beginning of the Permian Period and then dropped close to what our present day levels are at. Because sea levels were so much lower than they were during the early parts of the Paleozoic Era, large amounts of continental areas were exposed. And, with the enormous Pangaea landmass now almost fully formed, ocean currents were altered. This change had a huge impact on the climate. Climate changes were drastic with ice sheets and sea ice in the polar regions of Pangaea and vast deserts in the mid regions.

Tectonic Activities: By the end of the Permian Period, most of the landmasses had almost completely assembled together to form Pangaea. Pangaea stretched from the north polar region to the south pole.

Plant/Animal Life: Marine organisms were similar to those of the Carboniferous Period. When the world's climate conditions began to move from a moist environment to a dry environment, many of the planets and animals adapted to these new, dry conditions. Fossil evidence has shown that insects were the dominant land animals. Many of these insects had actually grown to fairly large sizes: flying cockroaches measures 8 cm in length, dragonflies had wing span of 20 cm, and myrapods were 2 meters long. Reptiles appeared in the late Carboniferous Period and in the Permian Period they began to diversify into different groups. One group was the squamates, which includes snakes and lizards). Another group was the archosaurs, which includes dinosaurs and flying reptiles. Reptiles evolved to have internal fertilization and amniotic egg. Synapsids also appeared during the Carboniferous Period and diversified in the Permian Period. Synapsids have similar features to those of mammals. Thus, they are sometimes referred to as “mammal-like reptiles”. The difference between synapsids and reptiles is that in synpasids, they only have one jaw bone whereas reptiles have two or three; synapsids also have a ball-and-socket articulation between the back of the skull and neck.

Permian Extinction: One of the most devastating mass extinction in history occurred at the end of this period. More than 80% of marine species became extinct. Land organisms were also hit hard. Most hit hard were the amphibians, reptiles, synapsids, and the insects. Plants hit hard were the gymnosperms and progymnosperms (like gymnosperms, but reproduced through spores). Plants and vegetation was actually hit so hard that coal seams are absent in the Triassic Period. The causes for this mass extinction are still being investigated but it is thought that perhaps a combination of events may have triggered this extinction. Events such as continents moving together to form Pangaea (caused a reduction of sea and seaways between continents); drop in sea levels (affected marine life who lived in the shelf areas); with the formation of Pangaea, environments changed drastically, with a more widespread desert environments forming; in addition, with the formation of Pangaea, extreme temperature fluctuations occurred; volcanoes were erupting in China and Siberia with emissions from the eruptions perhaps blocking sunlight from reaching Earth's surface and adding more carbon dioxide to the atmosphere. An impact by a meteorite may have accelerated the extinction of life.

Mesozoic Era: Age of the DinosaursThe Paleozoic Era ended with a mass extinction known as the Permian-Triasic Extinction (PTX). Even though this was one of the most devestating mass extinctions in history, life forms were able to diversify in many ways to fill the biological voids. Gymnosperms became dominant trees, which include cycads, ginkgoes, and conifers. Reptiles readily adapted to the drier environment first true terrestrial animals with improved lungs for an active lifestyle and waterproof skin that helped prevent loss of body fluids. They also developed shell-covered eggs that can be laid on land. The remaining ties to the ocean were broken. For nearly 160 million years, dinosaurs reined supreme. Some took to the skies (plerosaurs) and others returned to the sea while retaining teeth and lungs. At the end of the mesozoic era, ¾ of all plants and animals died out in a mass extinction (K-T boundary). Meteorites that hit the Earth in a region of now Mexican's Yucatan Peninsula and/or volcanoes eruptions in the Deccan Plateuo of Northern Indian are two hypothesis for the KT extinction.

Triassic PeriodPaleoclimate: Sea levels were low at the beginning of this Period and slowly rose in the middle of the period and back down at the end. Climate on land shifted to a more dry and arid conditions.

Tectonic Activities: Orogenies in Eurasia took place (Cimmerian orogeny and the Cathaysian orogeny). Pangaea was completed and east of it was the Tethys Ocean and west of it was the Pacific Ocean. At the end of the Triassic Period, Pangaea began to split apart. Rift basins in eastern North America formed and continued to grow through the Jurassic Period. Eventually the Atlantic Ocean formed.

A small continent (modern day Nevada, California, and Oregon) moved towards the North American continent. The collision between these two plates produced the Sonoma orogeny.

Plant and Animal Life: With the extinction at the end of the Permian Period, a new world was ready to be filled by those who survived. Conodonts and ammonoids were two marine organisms who survived the Permian extinction and evolved quickly during the Triassic Period. Clams, brachiopods, and snails slowly recovered from the Permian extinction. By the end of the Triassic Period, the oceans were once again filled with many different marine life. A new kind of fish was introduced in the Triassic Period called the teleost. Reptiles moved into the ocean during this Period including the nothosaurs, placodonts, ichthyosaurs, and plesiosaurs (who ended up living beyond the Triassic Period). Near the end of the Triassic Period, mass extinction greatly affected marine life. Causes of this extinction may have been due to the climate shifting to a more dry and arid conditions. A drop in sea level occurred. As a result, approximately 20% of marine families disappeared. Conodonts, nothosaurs and placodonts disappeared. Others suffered but survived. Life on land did not suffer as much from these climate changes. Gymnosperms dominated the land. Frogs, turtles, and archosaurs were introduced in this period. Archosaurs was a reptilian group who could stand or walk in an upright position. This was a first as previous reptiles were either in a squat or sprawling positions. This new feature opened the way for the evolution of upright posture. Archosaurs include reptiles such as crocodiles, phytosaurs, pterosaurs, and dinosaurs. Early dinosaurs were small and bipedal (moving on the rear two limbs).

Jurassic PeriodPaleoclimate: The Jurassic Period began with the sea levels being at its lowest ever recorded in history so far. Sea levels then began to rise early in this period.

Tectonic Activities: Pangaea was continuing to split apart. The breaking up of Pangaea led to the development of the modern day continents. After Pangaea was formed, it did not last long as a supercontinent. One idea is that Pangaea had moved over hot spots that caused crustal expansion and cracking (similar to what is going on in the African rift zone). The breakup of Pangaea caused a separation of biotas. As Pangaea continued to break apart, sea levels rose. There were several rifts that were taking place such as the Atlantic rift basin (from eastern Canada southward to the Gulf Coast); and a rift split up North America and South America, which opened up the Gulf of Mexico.

Animal/Plant Life: The Jurassic Period went though the third stage of the Mesozoic Marine Revolution. As a result of threatening preys in the ocean (plesiosaurs, ichthyosaurs) and above the sea (pterosaurs), many of the organisms developed thick shells with spines, developed camouflage patterns, or attached empty shells to their own shells. Squids developed the ability to release ink in the water.

Dinosaurs became rulers of the land and remained so through the Cretacious Period. Dinosaurs descended from the primitive archosaurs in the late Triassic Period. Originally, a “mammal-like” reptilian group, synadpsids, was more prominent, on land, but the extinction of many synapsids in the late Triassic Period allowed the dinosaurs to take evolutionary advantage.

Cretacious PeriodPlate Tectonic Activities: Pangaea continued to drift apart. The breakup and drifting accelerated during the Cretaceous Period. The division of Pangaea broke it into Gondwana (southern continents) and Laurasia (north continents). By the end of the Cretaceous Period, Gondwana broke into modern day Africa, Australia, Antarctica, Southern America, and India. Laurasia broke into North America and Europe. Three orogenic events took place in North America (Nevadian orogeny, Sevier orogeny, and the Laramide orogeny). Rifting and drifting of the plate tectonics resulted in ridge volume swells. This cause sea levels to rise around the world and flood continental shelves. North America's western region was covered in a shallow epeiric sea called the Western Interior Seaway. At the end of the Cretaceous Period, sea levels dropped. This reduced the shallow sea over continents.

Paleoclimate: Due to the undersea volcanic eruptions, a warming of the ocean occurred, which created a nice tropical environment for the planktonic microorganisms to bloom.

Plant/Animal Life: Due to the warm ocean conditions, seas were full of life. Diatoms, dinoflagellates, planktonic and benthic foraminifera, and coccolithophorids were going through a great evolutionary success. Coccolithophorids was a group of calcareous nannoplankton. Their skeletons blanketed the sea floor, forming thick layers of soft limestones called chalk. In the word Cretaceous, creta means chalk. The top marine predators were reptiles, such as the mosasaur, who was a marine lizard that reached 15 meters. On land, dinosaurs still ruled the land. Placentals and marsupials evolved by the end of the Cretaceous Period. Angiosperms had also evolved. Angiosperms had a huge advantage over gymnosperms as their seeds were enclosed in an ovary. They also have a starchy component to provide food for the seed. Angiosperms also did well because of the flowers, which attracted animals, especially insects. These animals helped to transport pollen and seeds, such as by eating the fruits and berries and then taking a shadobbey somewhere far away. A coevoltion took place between insects and angiosperms. Because certain insects were interested in certain types of flowers, rapid speciation led to changes in flowers. By the end of the Cretaceous Period, angiosperms became the dominant land plant.

Cretaceous Extinction: This great extinction had been in the making for several million years (unlike the general popular belief that it happened swiftly when the meteorite hit Earth). The ichthyosaur had already disappeared and other groups were also declining in numbers. The meteorite that struck Earth was just the last straw that helped speed up the decline in numbers. Causes of the extinction:

1) Major Volcanic Activities: The increase in dust levels caused light from the sun to be blocked, which prevented light from reaching photosynthetic plankton. In addition, hydrogen sulfide and nitrous oxide gases from the volcanoes combined with water vapors and may have produced sulfuric and nitric acid with may have poisoned some life forms.

2) Sea levels dropped at the end of the Cretaceous Period. Thus, continental shelves were now exposed and marine life who lived in these regions suffered because of this.

3) Global cooling caused many of the warm-marine organisms to die out. With many marine organisms dieing out, preys also began to diminish. Similarly, on land, plants also received less light, which affected herbivores, which in turn affected the meat eaters.

It was mostly the small animals who were the ones who survived these harsh conditions. The bolide that hit Earth crashed into the Northern region of the Yucatan Peninsula of Mexico. Mosasaurs, plesiosaurs, ammonites, and belemnites were just some of the creatures extinct from the seas. Ornithischians, dinosaurs, pterosaurs, and saurischians (except for birds) all became extinct.

Cenozoic Era: Age of Mammals/ AngiospermsDuring this Era, mammals replaced reptiles as dominant land animals. Angiosperms replaced gymnosperms as dominant plants (which in turn strongly influenced the evolution of bids and mammals). During middle tertiary, grasses developed rapidly and spread over the plains (which fostered the emergence of herbivores), which in turn established the evolution of large predatory mammals. During the Cenozoic, the ocean was teeming with modern fish (tuna, swordfish). In addition, some mammals (seals, whales, walruses) returned to the sea.

Paleogene PeriodPaleoclimate: Global temperatures rose and the world entered into a greenhouse phase. The world was so warm that lush forests grew in the arctic region. Antarctica, which had been a part of the Gondwana continent was left in the southern polar region. The warm waters, which had previously warmed the shores of Antarctica, now became trapped in a current system that flows around it, called the Circum-Antarctic Current. Eventually, this trapped water started to cool and Antarctica became colder and colder. Glaciers, which had previously been confined to small regions was now able to expand over Antarctica. By the mid-Oligocene, quite a bit of the world's water was trapped in the glaciers in Antarctica, which resulted in a drop of sea levels.

Tectonic Activities: The Laramide orogenic events resulted in the uplift of the Rocky Mountain of North America. This event was related to the Farallon Plate being subducted underneath the North American Plate at the Pacific continental margin. The suduction of the Farallon Plate was at a low angle so the actual uplifting took place far way from the margin.

Animal/Plan Life: marine life forms evolved and changed very little, but did become more numerous and diverse. Many of the life forms in the oceans are quite modern in their appearance. Some land mammals, such as whales, returned to the seas. On land, angiosperms, mammals, and insects continued to diversify. Birds experienced a great evolutionary expansion. Grass also went through a great evolution. Grass, an angiosperm group, was able to evolve the ability to grow continuously, which was great for the grazing herbivores.

Neogene PeriodPlate Activities: Plates had reached its modern configuration. With the collision of the African Plate with India and Eurasia, the Tethys Ocean was constricted and left behind the Mediterranean Sea along with other basins (Black Sea, Caspian Sea, and Aral Sea). Uplifting of the Colorado Plateau helped the Colorado River erode down its path, eventually forming the Grand Canyon (formed in less than 20 million years).

Plant/Animal Life:Sea life was composed of modern species, with many of the species still living today. Whales increased their species numbers and dolphins appeared. Marine vertebrates changed little during the Quaternary Period. On land, there were two factors that influenced the changes in the biota: the changing climatic conditions and the change in the food supplies. Herbaceous plants and grasses responded to the changes in climate. With changes in plants, a change in animals also occurred. For example, grasses in the past (C3 grasses, had less silica than C4 grasses). So, when C4 grasses became more prolific than the C3 grasses, grazing animals with longer teeth survived, whereas animals with shorter teeth went extinct (since C4 grass had more silica in it). Species of even-toed ungulates increased, whereas odd-toed ungulates declined in numbers.

Quaternary PeriodPaleoclimate: After a period of warm climate conditions in the Pliocene Epoch of the Neogene Period, the Northern Hemisphere entered into another Ice Age event. Glaciers expanded and contracted several times, spreading across North America and Europe. Global advance of glaciers began about 2,500 mya. Since then, global climate switched between cooled periods of glacial expansions and warmer interglacial episodes when the glaciers receded. Using preserved layers of ice from cores of glaciers, glaciologists are able to use each layer of the ice and study the changes in oxygen levels and atmosphere conditions, and so on, in each glacial episode. During Periods of glacier expansion, as much as 30% of the world may have been covered in ice. Glacial Ice expanded over the Northern Hemisphere and covered North America, Europe, and Asia to around the 40thparallel. In some areas, glacial sheets were as thick as 3 km. The weight of this glacial sheet compressed the continental crust, deforming the crust downward. Each time the glacial sheet retreated, the crust experienced isotsatic rebound. In fact, an isostatic rebound is taking place currently in some regions of the Northern Hemisphere, such as in the Great Lakes region. Initially, right after the ice sheets retreated, the crust uplifted rapidly (elastic). After this elastic phase, uplift is still taking place, at a much slower pace and may continue to uplift for another 10,000 years.

Each glacial advancement affected the land either by polishing the rocks, scouring V-shaped stream valleys into broad U-shaped valleys, creating lakes, changing rivers and lakes that already existed, and deposited rocks in moraines. In the last glacial episode, the Niagara falls was formed when the Niagara Escarpment was uncovered, allowing weak shales to be eroded by rushing water.

Each major glacial expansion resulted in a change in eustatic sea levels and changes in biotic patterns. For example, during a glacial episode, sea levels would drop as much as 100-120 meters. Many continental shelves that were underwater were now exposed. The Bering Straight turned into a land bridge called Beringia and connected Asia and North America. This event allowed animals and humans to enter the North and South American continents.

The epoch that we are in now, the Holocene Epoch in the Quaternary Period, is currently in an interglacial period.

Plants/Animal Life: Marine life is essentially fully modern in species and generic compositions. On land, large mammals, adapted to the cold-weather conditions in North America, died out at the end of the last glacial episode. Many of the land species are similar, but also different from those of their present-day relatives.

Human Evolution: Homidids is a primate group that includes australopithecines and species in the genus Homo. Homidids have a geologically short evolutionary history. Homidids first appeared in Africa between 6 and 7 million years ago. Hominids and apes evolved separately from a common ancestor that existed sometime in the early Miocene (20 mya). The genus, Homo, appeared in the Pleisocene Epoch (2.4 mya). They had a fairly large skull and smaller teeth (they were on their way to becoming modern day humans). Australopithecines appeared in the Miocene Epoch. They had more of a apelike skull with a small brain. Their skull was shorter than that of modern humans. In some places, the Homo and Australopithecines overlapped in geographic range. Homos, with their larger brains, had more of a competitive advantage.

b. Describe how earthquakes intensity, magnitude, epicenter, focal mechanism, and distances are determined from a seismogram

Seismograms revel two main groups of seismic waves. One type travels along the outer part of Earth and are called surface waves. Waves traveled through Earth's interier are called body waves. Body waves are divided into primary (P waves) and secondary (S waves).

P waves push-pull (compress and expand). P waves are compressional waves and can travel through solid, liquid and gas materials. Changes volumes. When P waves moves through rock mass, the rock mass will compress and expand. When the P waves moves on, the rock mass will return to its original shape (elastic strain).

S waves shake the particles at right angles to to their direction of travel. Changes shape. Gases and liquids do not respond to changes in shape so they do not transmit S waves. They have greater amplitude than P waves.

Surface waves (L waves) move up and down and side to side (this one is particularly damaging. Greatest amplitude.

So, on a seismogram, P waves arrive at the recording station first, then S, then surface waves. The greater the interval measured on a swismogram between the arrival of the first P wave and the first S wave, the greater the distance to the earthquake source.

Travel time graph were constructed to pinpoint epicenters. To determine the distance from the epicenter to the recording station by: 1( determine time interval between the arrival of the P wave and S wave 2) Use travel-time graph, find P-S interval on the vertical axis and use that info to determine the distance to the epicenter on the horizontal axis. So you find the direction by using three or more different seismic stations on a globe. We draw a circle around each seismic station. Each circle represents the epicenter distance for each station. The point where the three circles intersect is the epicenter of the quake. This method is called triangulation.

Intensity- use intensity scale that consider damage done to buildings and secondary effects (landslides and the extent of ground rupture). Guispeppe Mercalli developed the modified Mercalli Intensity Scale. This scale helps seismologists to compare earthquake severity but they are based on effects of earthquakes that depends on the severity of ground shaking and also factors such as population, density, building design, and nature of surface materials.

Magnitude- Charles Richter developed the first magnitude scale using sesmic records to estimate relative sizes of quakes. Based on amplitude of the largest seismic waves (P, S, L) recorded on a seismogram. Since seismic waves weaken as the distance between the earthquakes focus and the seismograph increases, Richter developed a method that accounted for the decrease in wave amplitude with decrease distances. Monitoring stations at various locations would obtain the same Richter magnitude for every recorded earthquake, although they would obtain slightly different Richter magnitudes due to the variations in rock types through which the waves traveled. Largest magnitude recorded on Wood-Anderson seismograph was 8.9.

c. Compare major types of volcanoes in terms of shape and chemical and rock compositions

ShieldProduced by accumulation of fluid, basaltic lava and exhibit the shape of a broad, slightly domed structure that resembles a warrior's shield. Most have grown from the ocean floor to form islands or seamounts. Mount Olympus on Mars is the largest shield volcano. Young shield emit fluid lava from a central vent and have sides with gentle slopes that vary from 1 to 5 degrees. Mature shields have steeper flanks (~10 degrees) with their summits comparatively flat and lavas are discharged from the summit vents and as well as rift zones that develop along the slopes. Most of the lava is discharged as the fluid pahoehoe, but as it cools during downslope may change into a aa flow. Since 80% flows through lava tubes, it can travel to the sea, thereby adding to the with of the cone at the expense of the height. Mature shield volcanoes have a large, steep-walled caldera which from when the roof of the magma chamber collapses when the magma reservoir evacuates or migrates. In the final stage of growth, the activity is more sporadic and pyroclastics ejections are more prevalent and the lavas increase in viscosity resulting in thicker, shorter flows, which steepens the slope, which becomes capped with clusters of cinder cones.

Cinder ConesAlso known as scoria cones, are built from ejected lava fragments that take on the appearance of cinders or clinkers as they begin to harden while in flight. These pyrclastic fragments range in size from fine ash to bombs that may exceed a meter in diameter. Most of the volume of cinder cone consists of lapilli that remarkably vesicular (containing voids) and have a black to reddish color. They sometimes extrude lava and on such occasion are discharged from vents located at or near the base. These are the most abundant of the three types of volcanoes. They have a simple, distinctive shape determined by the slope that loose pyrocalstic material maintains as it comes to rest. Cinders have a high angle of repose (steepest angle at which material remains stable) young cinders are steep-sided (30-40 degrees). They also have large and deep craters. Somewhat symmetrical, but one side may be higher because the side was downwind during the eruptions. Most are produced by a single short-lived erupture event where ½ of all cinder cones were constructed in less than 1 month and 95% is formed less than a year and some remain active for several years. Once they event ceases, the magma in the “plumbing” connecting the vents solidifies so that it never erupts again. Thus, they tend to be small (30m to 300m). They are found all over the world. Some are parasitic cones of larger volcanoes.

CompositeMost dangerous volcano. Most are found in the relatively narrow zone that rims the Pacific Ocean, called the Ring of Fire. This active zone consists of a chain of continental volcanoes along north and south Americas, Andres, Cascade Range, and Canada. The most active regions are located along curved belts of volcanic islands situated adjacent to deep-ocean trenches of the norther and western Pacific.

Nearly symmetrical composed of lava and pyrocalstic deposits. Products of gas-rich magma having an andesitic composition (may also emit various andesitic composition (may also emit various amount of material having a basaltic and/or rhyolitic composition). The silica-rich magma typical of composite cones generate thick viscous lavas that travel short distances. These volcanoes may generate explosive eruptions that eject huge quantities of pyroclastic material.

Typical growth begins with both lava and pyroclastic material being ejected. As it matures, lavas tend to flow from fissures that develop in the lower flanks of the cone. Lava flows alternate with pyroclastic ejection though sometimes they occur simultaneously.

Conical shape, steep summit area, and gradually sloping flank. Shape is due to the way viscous lavas and pyroclasic ejecta contributes to the growth of the cone. Course fragments ejected tend to accumulate near the source. Because of high angle of recourse, coarse materials contribute to the steep slopes of the summit area. Finer ejecta is deposited then layer over a large area, which acts to flatten the flank of the cone. In the beginning stage, lava flows further distances from the vent then later flows, which contributes to the cone's broad base. As the volcano matures, lava flows from the vent strengthens and armors the summit area. Thus, steep slopes exceeding 40 degrees are sometimes possible. Most composite cones have a complex history. Huge amounts of volcanic debris suggests that in the distant past, large sections of the volcano slid downslope as a massive landslide. Others developed horseshoes shaped depression at their summits as a result of explosive eruptions (80- mt st. Helen). Often so much rebuilding has occurred since these eruptions that no trace of amphitheater= shaped scar remains.

d. Describe the location and characteristics of volcanoes that are due to hot spots and those due to subduction

Stages of evolution of a volcanic island

Hot Spot VolcanoesAs ascending mantle plume enters the low-pressure environment at the base of the of the lithosphere, melting occurs. Hot spots form here, which has high heat flow and crustal uplifting that is a few hundred km across. As the pacific plate moves across this hot spot, successive volcanic structures are built. We now recognize that most interplate volcanism occurs where a mass of hotter than normal mantle material called a mantel plume ascends toward the surface. These plumes of solid yet mobile mantle rock rise toward the surface in a manner similar to the blobs that form within a lava lamp. Like the blob in the lava lamp, a mantle plume has a bulbous head that draws out a narrow stalk beneath it as it rises. One the plume head nears the top of the mantle, decompression melting generates basaltic magma that may eventually trigger volcanism at the surface. The result is a localized volcanic region a few hundred km across called a hot spot. More than 40 hot spots have been identified. The land around hot spots tend to be elevated, buoyed up by the plume of low-density material. Geologists have determined the mantle beneath the hot spot to be 100-150 degrees C hotter than normal. Basaltic lava. As the plume reaches the base of the lithosphere, temperature is established to be 200-300 C warmer than surrounding rock. Thus, as much as 10-20% of the mantel material making up the plume head rapidly melts. It is the melting that triggers the burst of volcanism that emits voluminous outpourings of lava to form huge basalt plateau in a manner of a million yeas.

Global distribution of volcanoes are not random. Majority are located among the ocean basins, most notably within the Ring of Fire, which consists of composite cones that emit volatile rich magma having an intermediate (andesitic) composition. As a slab of oceanic crust descend into the mantle, an ocean trench is generated. As this slab descends deeper, the increase in temperature and pressure drives volatiles from the ocean crust. These fluids migrate upward into the wedge-shape piece of mantle located between the subducting slab and overriding plate. Once the sinking slab reaches a depth of 100-150 km, these water-rich fluids reduce the melting points of hot mantel rock sufficiently to trigger some melting. The partial melting of mantle rock generates magma with a basaltic composition. After a sufficient quantity of magma has accumulated, it slowly migrates upward.

e. Relate geologic structures to tectonic settings and forces

Plate tectonics is one of the most exiting things that has happened over the last 30 years. It was a completely new understanding of the way in how the earth works. By the 70s the idea of plate tectonics was spreading. Part the reason why we didn't get it before was because we didn't have good idea of the ocean basis. Understanding the ocean basins triggered the theory of plate tectonics.

To put is simply, Plate tectonic states that most of Earth's internal processes (formation of ocean basin, mountain building, volcanic activity, faulting and earthquakes) and many external processes (circulation of ocean currents, glaciation, pluvial erosion) are controlled by the interaction of the thin, rigid plates that form the lithosphere

Stress: force per unit area, changes shape of rocks (deform)

Compressional Stress: causes rocks to shorten or flatten

Tensional Stress: causes rocks to stretch and elongate

Shear Stress: causes rocks to “smear”

Strain: deformation caused by stress. Three types of strains:

Elastic: Rocks can behave in an elastic manner when the rock material can recover its initial shape when stress is removed or reduced (example, P waves moving through a rock mass)

Plastic or Ductile: Rocks behave like plastic when the rock material bends but doesn't break (example, rock mass at plate boundaries in earth's interior). Takes place in wamer conditions.

Brittle: Rocks can be brittle if it breaks under stress (example, rocks subjected to t ectonic stress at plate boundaries) Takes place, near the surface of the lithosphere, granitic rocks, and cooler temperatures.

Fold: wave-like bends in rock. The top most part of the wave arch is called the anticline and the bottom part of the wave arch is called the syncline (I remember this by thinking that sincline and sink both start with the letter s). Oldest rocks are found at axial region of the anitcline due to erosion taking place. And vice versa for synclines.

Faults: Brittle fractures in rock mass along which movement has taken place

Dip-Slip Faults: these are faults that are primarily parallel to the dip of the fault surface. Movement is primarily horizontal. The rock surface above the fault is called hanging wall, and the rock surface below is called the footwall.

Normal Faults: when hanging wall block moves down relative to the footwall block. They have dips of about 60 degrees. Normal faults accommodate lengthening, or extension of the crust. Uplifted fault blocks are called horsts and down-dropped blocks are called grabens. Examples of normal fault block mountains include Teton Range and the Sierra Nevada.

Reverse Faults: The moving wall moves up relative to the footwall block. Reverse faults develop as a result of compressional tension.

Strike-Slip Fault:Faults in which the displacement is horizontal and parallel to the strike of the fault surface. The concept of headwall and footwall doesn't apply. The broken rocks produced from strike-slip faults are easily eroded and often form linear valleys and troughs.

Transform: a special kind of strike-slip fault that cuts through the lithosphere and accommodates motion between two large crustal plates.

Right-lateral Strike Slip: Opposite side of the fault moves to an observer's right (if the observer is facing the fault). The San Andreas is an example of a right-lateral strike slip fault.

Left-lateral Strike Slip: Opposite side of the fault moves to an observer's left (if the observer is facing the fault).

Joints: Joints are fractures that do not show evidence of slippage whereas faults do. Joints are the most common rock structures. Joints can occur as a result of pressure release, tectonic stress associated with regional uplift,

Divergent Boundary (constructive plate margin)

This is found along the crests of oceanic ridge. Within a divergent boundary, tectonic plates are being pulled apart, away from the ridge axis. Normal faults are common near the Earth's surface, where the lithosphere is cool and brittle. Fractures that formed are filled with molten rock that comes up from the mantle below. When this material cools, it forms new lithosphere. Examples: Mid-Atlantic Ridge (seafloor), East African Rift (continental rift)

Convergent Boundary (destructive plate margin)

Occurs when two plate margins move towards each other. Reverse and thrust faults are expected for form at shallow depths, where the rocks are cool and behave in a brittle fashion under compressional stress. At greater depths, folding may take place where it is warmer and under higher pressure. Three types of convergent boundaries:

Oceanic-Continental Convergence:

This particular convergent boundary occurs when the denser oceanic slab and the buoyant continental slab move towards each other. The oceanic slab sinks into the mantel. When this slab reaches a depth of around 100 km, melting occurs due to the “wet” rock in the oceanic lithosphere (wet rock melts at substantially lower temperatures). Partial melting takes place. The molten material is less dense than the surrounding mantle and thus gradually rises toward the surface, which may then give rise to a volcanic eruption.

Oceanic-Oceanic Convergence

When two oceanic slabs converge, one descends beneath the other, which initiates volcanic activity. The volcanoes grow up from the ocean floor. Eventually, as the subduction continues, a chain of volcanic structures will develop, called volcanic island arc.

Examples: Aleutian, Mariana, and Tonga islands

Continental-Continental Convergence

Continental lithosphere is buoyant so when two continental plates move towards each other, neither one is able to be subducted. Thus, a collision occurs and produces mountain ranges.

Example: Himalayas, Alps, Appalachians, and Urals.

Transform Fault Boundaries

This plate boundary occurs when two plates slide horizontally past each other. Strike-Slip Faults are common and wherever they bend, compressional and extensions can occur which may result in normal faults or reverse faults and folds.

Geologic structures are usually the result of the powerful tectonic forces that occur within the earth. These forces fold and break rocks, form deep faults, and build mountains. Repeated applications of force—the folding of already folded rocks or the faulting and offsetting of already faulted rocks—can create a very complex geologic picture that is difficult to interpret. Most of these forces are related to plate tectonic activity. Some of the natural resources we depend on, such as metallic ores and petroleum, often form along or near geologic structures. Thus, understanding the origin of these structures is critical to discovering more reserves of our nonrenewable resources.

f. Describe the evidence for plate tectonics on the sea floor and on land

Sea FloorEvidence for plate tectonics begins with paleomagnetism. Certain rocks contain minerals that serve as “fossil compass”. These iron-rich minerals, such as magnetite, are abundant in lava flows of basaltic composition. When these iron-rich grains cool below there Curi point (58 C for magnetite), then they gradually became magnetized in the direction of the existing magnetic line of force. Once the minerals solidify, the magnetism they posses may remain “frozen” in this position. So, around the same time of Hess' formulation on the concept of seafloor spreading, geophysicsts were beginning to accept the fact that over thousands of years, Earths' magnetic field periodically reverses polarity. So, when the rocks present magnetism and the present magnetic field, then it posses normal polarity, whereas when rocks exhibit the opposite magnetism, then its reverse polarity. According to Vine and Mathews, as magma solidifies along narrow rights at the crest of an oceanic ridge, it is magnetized with the polarity of the existing magnetic field. Because of seafloor spreading, this strip of magnetized crust would gradually increase in width. When Earths' magnetic field reversed polarity, any newly formed seafloor *having the opposite polarity) would form in the middle of the old strip. Gradually, the two parts of the old strip are carried in opposite directions away from the ridge crest.

LandEvidence for land plate tectonics:

The continents fit like a puzzle- if you look at the outer boundary of a continent, its continental shelf, they can be fit together.

Fossil- identical fossil organisms were known from rocks in both South America and Africa. Mesosaurus, an aquatic fish-catching reptile whose fossil remains are found only in black shales of Permian age (~260 mya) in East South America and South Africa. If it made its way across, then its remains would be more wildly distributed. Same with the fossil fern, Glossopteris. Its large seas was not easily distributed, but found on Africa, Australia, India, and South America, and Antarctica. And these plants are only known to grow in sub polar climate.

Similar Rock Types and Structural- Since continents were joined, it must mean that the rocks found in one continent must match those that are found in adjacent positions on the adjoining continents. 2.3 bya igneous rocks in Brazil closely resembles rocks in Africa.

Paleoclimatic- ice sheets covered extensive areas of South Africa and South America as well as India and Australia. Large tropical swamps existed in North Hemisphere.

About 4 bya, as much as 90% of the current volume of seawater was contained in the ocean basin. Primitive atmosphere was rich in CO2, as well as sulfur dioxide and hydrogen sulfide, so the earliest rain water was highly acidic. Thus, this caused accelerated weathering of Earths' rocky surface. Through the process of chemical erosion, products such as sodium, calcium potassium and silica were released. Some of the dissolved substances precipitated to form the chemical sediments that settled on the ocean floor, which others built up increased the salinity of the seawater. Today, seawater contains 3.5% dissolved salt (NaCl). Researchers say salinity increased rapidly, but has not changed dramatically in the last few billion years. The oceans also serve as a depository for tremendous volumes of CO2, a major constituent in the primitive atmosphere, and still to this day. Which is significant because CO2 is a greenhouse gas.

COMPOSITION OF SEA WATER

Water is a polar molecule: It has a positively charged end, and a negatively charge opposite end.

+ +

-

In comparisons, the comparable compounds, such as CH4 and H2S (only in gas form as it has a high freezing point) are symmetrical compounds and are non polar.

The water molecule has a tendency to attach to other water molecules. They are not very strong bonds between molecules (hydrogen bonds). But the don't move very far to bond with another molecule. Water is unique:

a. in its very high freezing point (0'c) and boiling point (100'C). Otherwise it would only exist in gas form if it weren't a non-polar.

b. it's very high specific heat and thermal inertia. It takes a lot more heat to raise the temperature of water than to raise the temperature of sand or a bunny. Water stores a lot of energy. Temperature is the measure of kinetic energy in a molecule. Give energy, it starts shaking, but because it has a strong attachment to each other, you need to raise a lot more heat to get it to break the bond. You need to take a lot of energy out to cool the water. A lot of heat can be stored in water. We have huge bodies of water, the oceans are the main repository of surface/shallow heat.

c. it's remarkable solvent capacity. Imagine two lovers: sodium and chlorine (salt). They stroll into a room where water is having a party. They are together because sodium has no pockets to store electrons, but chlorine does. So they are stuck together. They are attracted because of that charging balance. However, sodium, with its need for electrons, is surrounded by the hydrogen element part of water. And chlorine is also surrounded by water, but with the hydrogen part of water that is surrounding him, which are attracted to the chlorine. They pull on these lovers and now sodium and chlorine are split and broken apart (dissolved).

d. it's "odd" density changes. Normally, as you cool it down, the molecules get closer and closer and closer together, so it gets denser and denser. But as water because cooler, its molecules just rearranged themselves into this crystalline structure. This creates a structure of molecules with holes in it. Ice, the solid, is lighter, less dense than its own liquid. With that, it comes with all sorts of interesting properties. For example, when water freezes, it floats on top of a body of water. This layer of ice insulates the water below so that the animals can still live in the water and is shielding them from the cold. It is interesting to speculate what would happen if ice wasn't less dense than water (liquid form). Soon, a whole lake would be frozen and the animals would die.

Principals of thermodynamics:

Internal energy of a substance is the sum total of its kinetic (movement- how fast molecules are spinning and moving) and potential (stored) energy and molecule energy.

Temperature is a measure of the average kinetic energy. You can have a cup full of hot water, high temperature but small total internal energy. On the other hand you have the ocean with enormous volume with low temperature but high total internal energy.

Heat is the flow (flux) of kinetic energy from a hot to a cold substance. So if two things are the same temperature, then there is no heat, no flow of heat energy. Movement of heat always goes from the hot area to the cold.

If I start with a half a gram of ice, at the rate of about half a calorie per gram for every degree c I want to increase. So, for 20 degree increase I need to add 10 calories. At 0'c, the ice stays at zero degree, the heat I added to the ice goes to melting the ice, but not to increasing the temperature of the ice. This takes about 80 calories of gram to melt (takes a lot to break the hydrogen bonds). The moment the last grain of ice melts, then the temperature starts climbing, and it doesn't take much to increase the temperature of water. Then, you get to 100'c and another bizarre thing happens. It stops climbing. All the heat I keep adding (500 grams of calorie) to turn it to steam, remains a liquid. It takes an enormous amount of heat/energy to go through changes of phase.

1. Specific heat is the amount of energy we need to raise the temperature of a substance. For liquid water, it is 1 calorie/gram/degree C. Water has the highest specific heat of all of the substances. It requires more heat to raise its temperature and gives out the most heat when cooled.

2. Latent heat of fusion= latent heat of crystallization. Melting or crystallizing it, you have the same amount of heat. The transition of solid to liquid.

Yet, a glass left out at 20'c, evaporation still occurs, even if no heat is added. There are some molecules that still have higher than average kinetic energy so that it can still evaporate. The ocean evaporates large amount of water, yet it's not bubbling. The 540 calories is taken from the environment for the ocean to eject the molecules for evaporations. The energy to do this comes from the sun's solar radiation. Water has the characteristic that it allows penetration of solar radiation. The kinetic energy is being absorbed by the ocean in the photic zone (depth of penetration, approximately 30 meters down). Doesn't go very far because it scatters, and because all of the water has taken the energy. This energy taken in is storing an enormous amount of energy. So, those upper hundred feet is storing an enormous amount of energy. Now that energy is distributed upward to eject the molecules of water (vapor) and downward to the colder water (the liquid circulates).When the energy is being transferred to the main volume of the ocean (downwards), it does so through conduction or convection. Or, energy is being transferred to the atmosphere. The water vapor molecules will transfer some of its energy to the surrounding air. It increases the average kinetic energy of the air, hence increasing the temperature of the air. End result, is there is an enormous amount of thermal energy stored in the ocean. This evaporation is transferring kinetic energy into the atmosphere. It is the oceans that controls the temperature of the air, and it depends on how much solar radiation it receives. Air temperature does not control the ocean's temperature. At the equatorial region, it receives straight on UV rays. So, the equatorial water becomes quite warm. As this equatorial water circulates in a clockwise fashion, northward, it is giving off heat to the surrounding air, warming it up. That's why England and Ireland are habitable. But, the water is not getting much heat from the sun because it's further north where the Earth is at an angle from the sun. So, the water is giving off heat, but it's not regaining that heat as it continue its path. By the time it turns and moves back south, the water is cold. It has given off all of its heat that it had to the atmosphere. It will have to make a trip back to the equator to once again store that heat that the sun is able to give.

Salinity:Salinity is a measure of the amount of ions dissolved in water. So, if we would write this as 35 g/per L, average salinity of water= 35 parts per thousand (ppt), 35%= 35 practical salinity units (psu)= 35. White there are differences between each of these methods, we are going to assume at this time that they are similar. The range of salinity is between 30 and 39 ppt. And this is important to know. Mississippi would go from .1 to 1, 5, 10, 15 as you cross the river with the numbers increasing as you head out to the seas. Inland, it's smaller. Everyone knows that the ocean is salty, but there are variations, and these variations can effect the water cycle and the ocean's circulation. As you get close to the north pole, you reach the 30s, and in the middle of the planet, it's 39. There are high salinities along the Tropics of Cancer and Capricorn. The salinities are not high in the equator (fresh water has a tendency to well up in the equator). Basically, salinity is low where precipitation is greater than evaporation such as coastal and equatorial regions.

As you can see from this graph, river water is not as salty as ocean water. Top three big players of seawater is Chloride (Cl-), sodium (Na+), and sulfate (SO43-) in terms of dissolved ions. Whereas in river water, the big players are calcium (Ca3+), Bicarbonate (HCo3-) and Silica (SiO2). So, the ocean is not only saltier, but it also has a different composition than the river water that feeds them. This is a bit confusing as one would assume that the rivers are bringing salts to the ocean and that it is just a concentrated soup based on the water that rivers bring to the oceans. The difference is that calcium and carbonate is a great demand in the ocean. A lot of organisms take these two elements to form their shells, so it precipitates those elements out of the oceans. Algae take Si02 to make silica, their shells. And, no animals likes chlorine or sodium so that are the left overs--left over of three billion years of maturation of oceans. Actually, they are taken out. Rocks are coated with salt as it is splashed out and crystallized. High tide goes out during this time. Gypsum too (so4), precipitates and is removed from the seawater. A very small amount of gypsum is removed globally. Exceptions are the Gulf of Mexico. Before, it was a small isolated basin that got filled with water, and dried out, and then a new batch came in. If you drill in the Gulf of Mexico you find thick accumulation of gypsum and salts. Mediterranean at the bottom has a thick layer of salt and gypsum that was laid down when the water dried out a long time ago.

Nutrients:

PO4 3- 1ppm (found in very tiny amounts, but very important. algae food, high demand)

NO3 - 1 ppm (comes from Nitrates, atmospheric dilution, or from dusts that settles from volcanic eruptions, concentrated in the upper part of ocean)

Si02- 30 ppm runoff is not significant for phosphate and nitrate

Trace elements: (part per billion range)

Lithium (Li)

Iodine (I)

Molybdenum (Mo)

Zinc (Zn)

Iron (Fe): came into ocean through weathering of rocks

Aluminum (Al): carried to ocean by river water

Copper (Cu)

Manganese (Mn)

One source that made a small contribution of elements was probably the result of submarine hydrothermal weathering of rocks. Black smokers, where you have cold ocean water seeping through the cracks of the ocean land, seeping up from the cracks, is probably a big contribution.

Originally, it is thought that the ocean became got salty because rivers kept bringing stuff in, and evaporation carries water out, so the concentration grew. Now, the ocean is in chemical equilibrium and achieved this about 2 bya. Chemical equilibrium means that whatever water is bringing in, it is being taken out by sedimentation or biological activity. So, it's not becoming any more salty.

Gases:N2- source atmosphere- dissolved in ocean water because it is in contact with the ocean water

O2- largely photosynthesis, or the solution of oxygen into polar water

Co2- half of co2 in atmosphere and half from co2 created as respiration in organisms

Ar- gassing in black smokers and hydrothermal weathering of rocks

Oxygen is huge, important to life. But CO2 is the important key player, playing a very important role in oceans. In the upper levels of the ocean, nitrogen is the dominant gas, followed by O2 and Co2. Below, the clines, Co2 dominates the sea. The big bulk is Co2.

Buffering System So, you have HCO3- in the ocean. Most of the CO2 is dissolved in the ocean. In this complicated system, you have stuff that is coming in and out, but most will be stored as HCO3-. The loading dock is CO2 in the atmosphere. That's where a lot of CO2 comes from. It goes in and out of the water. Once in the water, it becomes C02 (aq) +H2O, which is actually dissolved in water, not just as bubbles. This forms a reaction to form H2CO3. There is a reaction between H2CO3 and HCO3-. One will turn into the other, and convert back again. By doing these conversions, hydrogen is generated. On the other side is another reaction going on. HCO3- also breaks down into CO3- + H+ and it also goes the other way, converting back to HCO3-. When CO3- + Ca2+ then it forms CaCO3 (calcite, shell of the bug). This shell falls to the bottom of the ocean floor and is removed from this chain of events. Each one controls the other one. So, if too much of this, then it will be removed by sedimentation. Or too much of that pushes the reaction to HCO3-. Oceans are crucial and holds an important role of maintaining the amount of CO2 in the atmosphere. They also have a control on the acidity of the ocean. The ocean is slightly on the alkaline side. So, the pH scale of water, 7.0, is the amount of hydrogen atoms in the water. Well, the ocean happens to be around 7.8, and it doesn't change much. Why? Because of the system in the ocean. It is buffered so well that if anything changes seriously, then the reactions turn the other way to maintain a constant amount of HCO3- + H+. You will also get the same value. Now, with global warming, CO2 will drive the reaction the other way. But, the ocean won't become more acidic. The system is buffered and retains it's acidity. The bad news is that this system will need a lot of time to change its reactions and turn it around. So, the CO2 content of the atmosphere could rise quite a bit, but the mixing happens at the sea surface interface and as large at the ocean is, it will need time to regulate the CO2. By the time the ocean has regulated the amount of CO2, we might not be around to see this.

b. describe the mechanism that cause wave action and tides

crest: the very top of a wave (the height of a wave can depend on the speed of the wind, the distance over which the wind blows, and the length of time the wind blows)

trough: the lowest part of a wave

wavelength: the horizontal distance between any one point on one wave and the corresponding point on the next

wave height: the vertical distance between the top of one wave crest and the bottom of the next trough

wave steepness: the ratio of height to length

amplitude: the maximum vertical displacement of the sea surface from still water level (half the wave height)

period: the time it takes for one complete wavelength to pass a stationary point

wave speed: the velocity with which waves travel

deep water waves: waves that are in water that is deeper than half their wavelength

shallow water waves: waves that are in water that is shallower than 1/20 their wavelength (the important difference on these last two is whether or not the sea floor influences the motion of the wave).

breaker: a collapsing wave

Two types of waves:

Body waves- waves that moves through a body

Surface waves- waves that moves at the surface

Surface Waves:

Waves that are formed at the interface of two fluids of different densities. Should really be called interface waves. Ocean has many interfaces. Oscillations that transmit energy and transmit energy much more than mass. Once it reaches shore, there is a transfer of mass. But way out at sea, deep waves, than there is not much transferring of mass taking place. Energy is transferred from the upper layer (wind) to the lower layer by shear stress. Water is forced to accelerate as the wind is moving fast over the crest, creating turbulence, and speeding up as it goes over the crest. Fast moving fluid exerts a much lower pressure than a slow moving fluid. So, this fast moving fluid causes a low in atmospheric pressure. The slow moving fluid causes a high in atmospheric pressure. Then a low, and so on. This is complimented by drop in atmospheric pressure as the air speeds over the crests (following Barcarole's Principal). Within the wave form energy is converted from potential energy to kinetic energy <----> back and forth. Imagine that you have water, a crest. The water has a certain energy and attraction of water molecules. It has a tendency to go down and starts converting potential energy into kinetic energy. It doesn't know that it has to stop at the mean valley. As it overshoots its mean value, it starts converting kinetic back into potential energy. Storing itself as potential energy and then it starts moving back up again. Think of the wave as a trampoline. A trampoline in its rest state is just sitting there. When you push on it, you create a storage of surface tension. Also storing potential energy. Lowering that membrane of its rest base. When you let go, it bounces up, but goes beyond is base level and bounces back up until energy has dissipated and comes to a rest.

How much waves are going to be generated depends on:

wind velocity

wind duration

fetch (distance over which the wind blows)

Different wavelengths are generated. Short wavelengths move the slowest and long wavelengths move the fastest. So, as these different sized wavelengths are formed, some will overlap, superimposed will occur.

A swell= waves generated far away, can travel 6,000 km without losing much of its character.

Wave Action:

Waves are energy that is carried through matter or space by a rhythmic movement.

Waves travel because gravity pulls the water in the crests downward. Forced out from beneath the falling crests, the falling water pushes the former troughs upward, and the waves moves to a new position, as indicated. (Notice that the actual motion of the water itself is circular or orbital). Unless there is a barrier, waves can travel across an entire ocean basin. Waves continue to form and increase in height as long as the wind is blowing.

The most familiar ocean waves are caused by the wind, called wind-driven waves. Energy transferred from the wind is transferred into the topmost layers of water as a result of friction and pressure. This is transported through the sea water. However, it should be noted that it is the waves that move, not the water itself.

Waves caused by underwater disturbances (such as earthquakes, landslides, or volcanic eruptions) are called tsunamis.

The gravitational pull of the sun and moon on the earth causes the tides, called tidal waves.

One wave motion is completely independent of any other wave motion. When two groups of waves meet, they pass right through each other (like light or sound waves, one doesn't garble the other). Waves can add up or cancel each other out as they pass through one another. This property is called superposition. If a crest and a trough line up, then the waves cancel each other out. This is called a destructive interference. If two waves line up, crest to crest, then they add up. This is called constructive interference. This is why the waves at beaches are of different sizes, since there are different types of waves coming in.

Tides:Tides is the passage of a standing waves caused by the gravitational attraction of the sun and the moon on the Earth and its oceans. The moon has the biggest influence since it is closer. It essentially pulls up a bulge in the ocean on the side of the Earth closest to it. There is a bulge on both sides of the earth (due to the force of the moon's pull, and the other side of the earth has a bulge because of the centrifugal force, the ocean on the opposite side of the earth is sort of thrown outward, like you are when you go around a bend in a car). So, as the moon revolves around earth, the earth experiences high tide about every 6.5 hours. So, in a 24 hour, perfectly ideal water world, you would have these two bulges twice every day.

Semidiurnal tides include two high tides and two low tides each day

Diurnal tides just has one high tide and one low tide per day.

The sun tugs on the oceans too, but has a less powerful effect than the moon. When the moon and sun lines up, then the result is extra high tides and extra low tides (a big tidal range). This event occurs twice a month during full and new moon) and are called spring tides. In between these, during the quarter phases of the moon, when the sun and the moon are not lined up with each other, we get tides with the lowest ranges, called neap tides.

Tsunami WavesTriggered by a sudden change in the volume of an ocean basin. This change in volume is important because there's plenty of earthquakes that don't trigger a tsunami. Earthquake are faults that cause a displacement in the ocean floor. The fault moving triggers the tsunami, not the earthquake.

Triggered by

a fault breaking through the ocean floor (triggers both an earthquake and the tsunami)

landslide into the ocean basin

A large submarine eruption. An example of one of the largest tsunamis that we know of took place due to the eruption of Krakatoa. This was a volcanic island that had erupted. There was no tsunami because the eruption itself as it didn't displace the ocean's volume. The collapse of the volcano formed a caldera and it was this that caused the tsunami. The eruption itself didn't cause the earthquakes.

a meteorite impact. One example is when the meteorite hit the earth that helped cause mass extinction of the dinosaurs (PTX?). The meteorite hit just off shore of Yucatan and produced a tsunami that swept through northern Mexico and Texas, a good 100-200 inland and we can still see this effect today.

c. Explain the layered structure of the oceans, including the generation of horizontal and vertical ocean currents and the geographic distribution of marine organisms, and how properties of ocean water, such as temperature and salinity, are related to these phenomena

Cold water rise to the surface in upwellings. As surface water moves out from the shore, cold water rises to take its place.

The Coriolis effect is caused by earth's rotation. This causes currents south of the equator to move in counterclockwise motion.

The west coast cold surface currents originates near the poles. Thus, warm surface currents (which originates at the equator) affects the water temperature along the east coast of continents.

When salt water changes in density, a density current occurs. Density currents are produced when seawater freezes. It also forms from an increase in salinity, decrease in temperature, and sinking of cold water.

Seawater density is affected by freezing of water, evaporation, and heating.

An upwelling occurs when the wind blows along the coast moving water away from the shore.

The upper portion of the ocean is a well mixed layer. As you travel further down, you will notice a fast change in the temperature of the ocean as the temperature drops. Further below, the temperature of the ocean becomes very cold. There is a region of a rapid change. This region is called a thermalcline.

Pressure increases steadily as you go down into the ocean. No, big swift changes. Pressure is due to weight of water. We are here at surface at atmosphere pressure. Every 10 meter you go down, is another atmospheric pressure.

Salinity goes from being very salty to disgustingly salty. Very frequently, salinity (homogeneous) has low salinity at the equator (due to lots of rain diluting sea water), as you move away from the equator you'll notice it becomes saltier water. Saltier water is denser, so it becomes heavier. So, the region where you get fast change is called a Halocline (for the word halite, salt), and you have another halocline further away from the equator. Density is related to both temperature and salinity. Salinity is the dominant feature of density. So, density changes little in the upper portion of the ocean, and then increase as salinity increases, then increase slowly. Sharp fast change for the density is called a Pycnocline. And another one further on, pycnocline. Salinity and temperature affects the density of water. As you increase the temp, salinity increases. The density of water is affected by its salinity content and its temperature.

Dissolved oxygen is pretty high in the uppermost portion of the ocean because you have a lot of plant materials that are photosynthesizing oxygen. Plus, that's where the atmosphere mixes with the ocean. But, as you get deeper from the zone of light, the photic zone (about 100 meters), it starts declining because there's no longer plants producing oxygen. So, that drops the level of oxygen quite a bit. Then, you get to a depth where's there's not much anything. No consumption of oxygen. But then oxygen level starts increasing a bit again. Interestingly, some of the highest oxygen content of the ocean is found at the very bottom. Oxygenated polar water sinks and hugs the bottom of the ocean. One exception are ocean basins blocked from circulation of polar water. Example would be the black sea. It's a closed basin that has no access to any of the large oceans so oxygenated polar water cannot get to it. So the lower part of the black sea isn't oxygenated since it cannot be replenished.

There is a relationship between the solubility of oxygen in water and temperature of the water. At low temperatures, you can dissolve more oxygen in the water. Cold waters are richly oxygenated. As temperatures increase, the solubility of water decreases. It is very cold at the polar regions, and hot at the equator. That means, the water at the polar regions have high oxygen content whereas the equator region has low oxygen content. Polar water also has a higher density, while the equator has low density. Because of that, polar water has a tendency to flow into the deep oceanic water at the equator. On the surface you just have hot water that lacks oxygen.

Warm water and water with higher pressure conducts sound at a much higher velocity. The sharp drop in temperature at the thermocline causes sharp drop in the velocity of sound, but the sound recovers because pressure becomes a mores significant feature. This is called the SOFAR. As a whale swims in the upper layers, it sends out sonar, looking for love. As it hits the zone of the SOFAR layer, the sound refracts into the layer. Same with a submarine sonar. Let's say another sound hits the zone at a very low angle, it can only reflect. So, sound gets trapped in the low velocity layer. It sends a sound signal and it is refracts and changes direction into it. Once it is trapped in this layer, it can go around the Earth and you can hear clear on the other side of the Earth. Which is why the mating call of whales are so successful.

a. Compare the layers of the atmosphere in terms of chemical composition and thermalstructure

layers of atmosphere in respect to altitude

<WILL POST PICTURE>

What defines the boundaries in the atmosphere is the temperature. There are five main layers of the atmosphere.

Temperature Variations

The troposphere, closest to earth, is warmest closes to the earth (Earth is heated from below (oceans, inner earth) and decreases with increased elevation. There is a reversal of temperature gradient within the troposphere layer. The boundary between the troposphere and the stratosphere is called the tropopause. Density has become very, very low at troposphere layer. Most of the mass of the atmosphere is in the troposphere. So, conveyance of heat, temp, most of the filtering effects of the atmosphere happen in the troposphere (except for ozone in stratosphere).

In the stratosphere, the temperature increases as you go higher. This increase in temperature is due to the absorption of radiation by the ozone layer, which is found in the stratosphere. The stratopause is the boundary between the stratosphere and the mesosphere.

The mesosphere isthe layer where meteorites are burned up upon entering our atmosphere. High energy cosmic reactions happen. So, ions here are electrically charged. Very important for telecommunications as they bounce off the electrically charged boundary and allows signals to come back down to earth. The electrical boundary is called the mesopause. Temperature decreases with altitude, and the coldest place on earth is found in this layer with temperatures dropping to -100 C at the mesopause.

Temperature increases with height through the Thermosphere. Still freeze to death. Not enough of the impacts to remain warm.

Composition

The air of the atmosphere is composed of a stable mix of 78% nitrogen, 21 % oxygen, and 1% argon, with trace amounts of other gases such as water vapor, carbon dioxide, methane, and ozone.

b. Discuss the evolution of Earth’s atmosphere over geologic time, including the effects of outgassing, the variations of carbon dioxide concentration, and the origin of atmospheric oxygen

When Earth's atmosphere was first formed, it may have consisted primarily of hydrogen, helium, methane, ammonia, carbon dioxide, and water vapors. There was no free oxygen in the atmosphere yet. Hydrogen and helium gases probably escaped into the space early on due to the fact that these gases were too light to be held by earth's gravity. Many of the other gases may have been blown off of earth by solar winds from the young and active star (many young stars go through this phase in the evolution of their lives called T-Tauri phase. During this phase, solar winds are very active).

Earth's atmosphere was first formed through a process called outgassing. Outgassing occurs when gases are trapped in a planet, Earth's interior, and released into the atmosphere. This outgassing is still occurring today through volcanic activities and eruptions. Gases emitted today are probably similar to the ones emitted in Earth's early life. Gases emitted by volcanic activity includes 35-90 % water vapor, 5-30 % carbon dioxide, 2-30 % sulfur dioxide, and trace amounts of nitrogen, chlorine, hydrogen, and argon. Thus, the early atmosphere must have consisted primarily of water vapor, carbon dioxide, ans sulfur dioxide, with trace amounts of the other gases.

Oxygen formed later in Earth's life. As the earth began to cool, water vapors in the atmosphere was able to form into water droplets and form clouds. This resulted in rains and began to fill low-lying areas with water, eventually forming the oceans. Eventually, approximately 3.5 bya, oxygen was formed in the oceans where photosynthesis began to take place. One of the earliest bacteria, cyanobacteria, began to produce oxygen through photosynthesis (which is the process of using sun's energy, carbon dioxide and water-although it is thought that early on, hydrogen sulfide was used instead, to produce oxygen). Oxygen readily joined up with iron to form iron oxide. The source of iron was found at submarine volcanoes. Thus, the iron oxide formed on the ocean floor and formed layers of iron rocks and chert called banded iron formation. Once iron had precipitated and the amount of organisms using oxygen increased, oxygen then began to accumulate in the atmosphere. Oxygen could have been found in the atmosphere as early as 2.2 bya. The amount of oxygen slowly increased and became stable at around 1.5 bya. Eventually, as the oxygen molecules were bombarded by ultraviolet radiation, it formed ozone, which eventually formed the ozone layer (which helped to protect earth from solar radiation for the first time ever).

c. Know the location of the ozone layer in the upper atmosphere, explain its role in absorbing ultraviolet radiation, and explain the way in which this layer varies both naturally and in response to human activities

The ozone layer is found in the lower portion of the stratosphere of the atmosphere. This layer formed billions of years ago when oxygen was first being bombarded by ultraviolet radiation. This bombardment caused the oxygen molecules to rearrange themselves to form O3, ozone. This formed the ozone layer which helped protect the earth from harmful solar radiation.<Human activity:>

d. Identify the bands at specific latitudes where rainforests and deserts are distributed and the causes of this pattern

Low-Latitude Desertsare found approximately 30 degrees north and south of the equator, in the Tropics of Cancer and Capricorn. The cause of these deserts being formed at these latitudes to due to the global distribution of air pressure and winds. At the equator, warm air rises (heated air in this pressure belt is called equatorial low). When warm air rises to great heights, it cools and expands, which leads to the formation of clouds and precipitation. This is why this region, the equatorial low, has rainforests, and is known to be the rainiest on Earth. As the air sinks above the 30 degree latitude regions north and south of the equator, it is compressed and warmed. As a result, this region is dry, sunny, and has very few rain (thus, ongoing drought).

Middle-latitude deserts are formed due to the fact that they are found in the interiors of a large landmass. For one, they are so far from oceans that they are deprived of moisture (which oceans provide) to produce clouds and precipitation. Another reason is because there may be a presence of mountains in the path of the prevailing winds. As air moves up a mountain, windward side, it expands and cools, forming clouds and precipitation, but as the wind moves over and down on the other side of the mountain, leeward side, it compresses and warms up, it is dry and lost its moisture. This often results in a rainshadow desert. Thus, for middle-latitude deserts, it is an example of tectonic force that affects climate.